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Radiation has affected animals living near the site of Ukraine's Chernobyl nuclear disaster far more than was previously thought, says a new study.

The study, which appears in the Royal Society journal Biology Letters, shows that numbers of bumble-bees, butterflies, spiders, grasshoppers and other invertebrates were lower in contaminated sites than other areas because of high levels of radiation left over from the blast more than 20 years ago.

The findings challenge earlier research that suggested animal populations were rebounding around the site of the 1986 Chernobyl explosion, which forced thousands to abandon their homes and evacuate the area.

Estimates of the number of deaths directly related to the accident vary. The World Health Organisation estimates the figure at 9000 while the environmental group Greenpeace predicts an eventual death toll of 93,000.

"Ours was the first study to focus on the abundance of animal populations."

Researchers say they had compared animal populations in radioactive areas with less contaminated plots and found that some were nearly completed depleted of animal life.

"There are areas with an abundance of 100 animals per square metre," Moller said. "And then there are areas with less than one specimen per square metre on average; the same goes for all groups of species."

High incidence of deformities

The researchers also found that animals living near the Chernobyl reactor - which was covered in a protective shell after it exploded in April 1986 - had more deformities, including discoloration and stunted limbs, than normal.

"Usually (deformed) animals get eaten quickly, as it's hard to escape if your wings are not the same length," says Moller. "In this case we found a high incidence of deformed animals."

The findings challenge the view of Chernobyl as ecologically sound, despite the fact that Ukrainian officials have turned it into a nature reserve, with wolves, bison and bears.

Earlier research into the area ignored the fact that animal populations had grown unimpeded in the absence of humans for many years after the blast, says Moller.

"We wanted to ask the question: Are there more or fewer animals in the contaminated areas? Clearly there were fewer," says Moller, who has studied Chernobyl since 1991.

While researchers focused on the 30 kilometre radius around the Chernobyl reactor, the fallout from the explosion covered a vast swathe of Eastern Europe, including parts of Russia, Ukraine and Belarus.

The findings probably apply to those areas as well, says Moller, adding that any decontamination effort was unlikely due to the extent of the fallout.